New kind of camera can image mini-tornadoes in quantum liquids

The camera set-up. The copper part is where the 25 cavities sit (see main story)

Researchers have built a camera-like device for understanding how vortices form in quantum liquids, where atoms pair up and start to behave like overlapping waves.

Vortices that form in quantum liquids can now be studied with a camera that uses particle-like disturbances to take images instead of light. Normal cameras can’t capture these whirlpools, so the device may lead to a more detailed understanding of how they form.

Swirl a spoon in a cup of tea and you can easily create a vortex. But researchers have long struggled to predict exactly how these tiny tornadoes form or how they will behave once you remove the spoon. The situation is simpler for vortices in quantum liquids, where pairs of atoms start to behave like a bunch of overlapping waves. That’s because these vortices always have the same size due to quantum effects that only arise at very cold temperatures. But there’s a problem: vortices in quantum liquids are too small to be imaged with conventional cameras.

Theo Noble and his colleagues at Lancaster University, UK have now created a new type of camera to observe their behaviour.

The camera records 25 pixels using 25 millimetre-sized cylindrical cavities, each with a quartz tuning fork in the middle. Disturbances in the fluid called quasiparticles don’t get caught in the vortex but instead affect the tuning forks in a way that can be measured.

“The whole experiment is kind of like shining a torch at the quantum vortices, then looking at the shadow,” says Noble. The work is set to be published in the journal Physical Review B.

The team tested the camera on vortices created by a vibrating wire in a form of ultracold helium. Even with its low number of pixels, the new camera uncovered that most vortices form above the vibrating wire instead of developing all around it. This was not predicted by mathematical theories or numerical simulations, says team member Viktor Tsepelin.

Carlo Barenghi at Newcastle University, UK says that this camera is the only currently available device for imaging vortices in this kind of ultracold helium.

Tsepelin’s goal now is to build a 90-pixel camera with a high enough resolution to image the motion of every individual vortex in a helium sample in detail.

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